1. Field of the Invention
The present invention relates to a process for the production of polyamide, including nylon 6,6 and nylon 6,6 containing low levels of comonomer, by reaction of adiponitrile with hexamethylene diamine in the presence of water.
2. Description of Related Art
Commercially, nylon-6,6 is made by the reaction of adipic acid with hexamethylenediamine (HMD). However, it is also known that polyamides, such as nylon-6,6, can be produced by reaction of diamines and dinitriles in the presence of water. Several patents address processes directed at such a reaction.
U.S. Pat. No. 2,245,129 discloses a process for the production of a linear polyamide polymer by a process which reacts adiponitrile (AND), HMD, and water at high temperature and pressure to produce nylon-6,6. The examples of this patent show reaction in a heated closed reaction vessel. The reactants were allowed to cool and then heated so that ammonia and water were vented from the vessel.
U.S. Pat. No. 3,847,876 discloses a process for the production of polyamides by reacting a diamine with a dinitrile in the presence of a controlled amount of ammonia. This process uses pressures of up to 2000 psig (13.7 MPa).
A number of patents disclose improvements of the aforementioned processes by use of a catalyst to promote formation of nylon. See for example, U.S. Pat. Nos. 4,490,521, 4,542,205, 4,603,192, 4,725,666, 4,749,776, 4,436,898, 4,501,881, 4,528,362, 6,075,117, and 6,103,863.
U.S. Pat. No. 5,627,257 discloses a process where in a first step, AND is hydrolyzed in the presence of water, catalyst, and 0 to 10 weight percent of the total HMD needed for the reaction. In a second step, the remainder of the HMD is added and the polymerization allowed to proceed. This two step process requires long process times.
U.S. Pat. No. 6,103,863 discloses a process for the production of polyamide from dinitrile (such as AND) and diamine (such as HMD) by a two-step process. First, the dinitrile is contacted with water and a catalyst to obtain at least 95% hydrolysis of the dinitrile. The reactor is purged of water and the ammonia produced by the reaction. Second, the diamine is added to the reaction and polymerization is allowed to occur. For this process the reactor design is not critical. Stirred autoclaves, unstirred autoclaves, column reactors, tube reactors, and loop reactors are given as examples of suitable reactors. The process has a disadvantage in that it requires the use of a catalyst and the use of either multiple reactors or interrupted addition of reactants to a single reactor.
U.S. Pat. No. 6,021,096 discloses a process for the production of a polyamide by reaction of an omega-aminonitrile with water in a vertical multistage reactor that is swept by steam. For example, this patent discloses a process to convert 6-aminocapronitrile to nylon-6. The process has a disadvantage in that it requires that the amine reactive group and the nitrile reactive group be part of the same reactive molecule (the omega-aminonitrile). Because hydrolysis of the nitrile group takes place throughout the reactor, the amine group is susceptible to degradation reactions caused by the conditions required for nitrile hydrolysis.
It would be desirable to have a process for making polyamide (including both nylon 6,6 and nylon 6,6 that contains some comonomer) that can be carried out (1) with or without catalyst, (2) in a single reactor, without interrupted introduction of reactants to the reactor and (3) using one reactant that contains a nitrile reactive group and a different reactant that contains an amine reactive group, so that the nitrile group can be hydrolyzed without adversely affecting the amine group.
The present invention is a continuous process for the manufacture of nylon 6,6 from adiponitrile (AND) comprising the steps of:
a) providing a vertical countercurrent multistage reactor having a top and a bottom, and having upper stages and lower stages, said reactor being equipped with internal perforated barrier means for establishing a plurality of stages and for effecting contact of an AND-containing stream and a countercurrently-flowing steam stream;
b) introducing into said reactor an AND-containing reactant stream at an AND introduction point near the top of said reactor;
c) introducing into said reactor a steam-containing stream at least one point near the bottom of said reactor;
d) introducing into said reactor a hexamethylenediamine-containing stream at least one point below the AND introduction point;
e) maintaining a pressure within said reactor between 100 and 800 psig (0.69 and 5.52 MPa) and a temperature at the top of said reactor between 190 and 250 degrees C and a temperature at the bottom of said reactor between 260 and 290 degrees C;
f) withdrawing a steam and ammonia-containing stream overhead of said reactor;
g) recovering a nylon 6,6-containing product stream from the bottom of said reactor;
wherein in said process the introducing of the AND-containing reactant stream and the introducing of the HMD-containing stream are adapted to provide a nylon 6,6-containing product stream in which the nylon 6,6 is characterized by balanced amine and acid ends.